The present invention relates to polishing apparatuses, and relates in particular to a polishing table for providing a flat and mirror polished surface on a workpiece such as semiconductor wafer.
Advances in integrated circuit devices in recent years have been made possible by ultra fine wiring patterns and narrow interline spacing. The trend towards high density integration leads to a requirement of extreme flatness of substrate surface to satisfy the shallow depth of focus of a stepper in photolithographic reproduction of micro-circuit patterns. A flat surface can be obtained on semiconductor wafer by chemical-mechanical polishing using a polishing table and a wafer carrier to press the wafer surface on a polishing cloth mounted on the polishing table while supplying a polishing solution containing abrasive particles at the polishing interface.
An example of the conventional polishing apparatus is shown in FIG. 9. A polishing table 12 capped with a polishing cloth 10 is used in conjunction with a top ring (wafer carrier) 14 for holding and pressing the wafer W onto the rotating top ring 14 with an air cylinder. Polishing solution Q is supplied from a solution nozzle 16, and the solution is retained in the interface between the cloth 10 and the bottom surface of the wafer W to be polished.
In such a polishing apparatus, heat is generated by friction between the wafer W and the cloth 10, and a pair of the heat is carried by the polishing solution while the remainder is transferred to the top ring 14 and the polishing table 12 and is removed by a cooling mechanism provided in these devices. A structural configuration of the polishing table 12 is shown in FIG. 10, which shows that the circular interior of the polishing table 12, made of stainless steel, has a spiral fluid passage 18 for flowing a thermal medium supplied through concentric shaft passages 22, 24 formed in the interior of a shaft 20. A rotary coupling is used to transport the thermal fluid from an external source through the passages 22, 24.
In chemical-mechanical polishing in general, and especially when using an acidic or alkaline solution, the rate of material removal is dependent sensitively on the temperature at the polishing interface. Therefore, in order to improve the uniformity of material removal across the surface of the wafer W, it is desired to control the polishing temperature distribution uniformly or in accordance with a predetermined temperature distribution pattern by controlling the flow rate of the fluid medium flowing through the spiral fluid passage 18 in the polishing table 12.
However, because the polishing table 12 is made of stainless steel in the conventional polishing apparatus, thermal conductivity is low, and it has been difficult to control the temperature of the polishing table 12 to provide the desired degree of thermal response characteristics. Also, the simplistic unidirectional flow pattern of the thermal fluid passage 18 results in a time lag for transferring heat between the center region and the outer region of the polishing table 12, and presents a problem that the polishing table 12 is unable to control individual temperatures of different regions of the turntable that are subjected to different polishing conditions.
It is an object of the present invention to provide a polishing apparatus able to strictly control the degree of material removal by providing close control over the operating temperature in the polishing table.
The object has been achieved in a polishing apparatus comprising a polishing table and a workpiece holder for pressing a workpiece towards the polishing table, the polishing table having a polishing section or a polishing tool attachment section at a surface thereof and a thermal medium passage formed along the surface, wherein the thermal medium passage comprises a plurality of temperature adjustment passages provided respectively in a plurality of temperature adjustment regions which are formed by radially dividing a surface area of the polishing table.
Accordingly, the lengths of individual passages are shortened so that the thermal medium passes through the passages quickly without experiencing much temperature variation, thereby stabilizing the polishing interface temperature and enabling the quick reflection of temperature control changes to the actual table temperatures to improve startup time and responsiveness of the polishing system. Also, because the flow of the thermal medium can be controlled for individual regions of the polishing table, finely-tuned temperature control can be performed to suit local changes encountered in the various regions of the polishing table.
The thermal medium passages may include two temperature adjustment passages extending from a mid-radially disposed fluid entry port, such that one passage extends to a center of the polishing table while other passage extends to a periphery of the polishing table.
Accordingly, since the passage is divided into two sections of shorter lengths, the time required for the thermal medium to pass through the passages is lessened, thereby enabling the quick reflection of temperature control changes to the actual table temperatures to improve startup time and responsiveness of the polishing system. Also, because the thermal medium flows into the region of the table where polishing is performed, temperature control of the workpiece can be achieved quickly.
The apparatus may be provided with flow adjustment valves for individually controlling fluid flow rates in the temperature adjustment passages.
The apparatus may be provided with temperature adjustment means for individually controlling temperatures of thermal media to be supplied to the temperature adjustment passages.
The apparatus may also be provided with sensor means for measuring temperatures in various locations of the surface region and flow control means for controlling individual flow rates of thermal media flowing in the temperature adjustment passages.
In another aspect of the invention, a polishing apparatus comprises a polishing table and a workpiece holder for pressing a workpiece towards the polishing table, the polishing table having a polishing section or a polishing tool attachment section at a surface thereof and a thermal medium passage formed along the surface, wherein at least the surface region of the polishing table is made of a material of high thermal conductivity. Preferred materials include SiC which has a thermal conductivity higher than 0.06 cal/cm/s/xc2x0 C.
In another aspect of the invention, a polishing table has a polishing section or a polishing tool attachment section at a surface thereof and a thermal medium passage formed along the surface, wherein the thermal medium passage comprises a plurality of temperature adjustment passages provided respectively in a plurality of temperature adjustment regions which are formed by radially dividing a surface area of the polishing table.
In the present polishing apparatus, because individual flow rates in various regions of the polishing table can be controlled, finely-tuned temperature control can be carried out to suit variations and changes in local polishing conditions. Temperature control is further enhanced by selecting a material of high thermal conductivity for at least those parts associated with the surface region. Heat transfer rate from the thermal passages to the surface region is facilitated so that thermal lag time is reduced and responsive temperature control can be achieved. Therefore, the present polishing system provides superior polishing in a variety of situations, thereby presenting an important technology for manufacturing of highly integrated semiconductor devices.